Usually when I see numbers this low, someone is filling up, and using gas tank capacity- 14 gal- to divide and figure fuel economy. The proper method is to fill up, hit the trip odo, then when you fill up again, divide the mileage on the trip odo by the number of gallons displayed on the gas pump.

Nearly every Focus we've asked about shows E (light comes on) when the tank has used about 10 gals leaving approximately 4 gals in reserve.